1. Field of the Invention
The present invention relates to methods for adjustment of a hearing aid, and to a hearing aid having a microphone system with a variable directional characteristic for reception of an acoustic input signal and emission of at least one microphone output signal, having a signal processing unit and having an output transducer. The invention also relates to a programmer for a hearing aid.
2. Description of the Prior Art
Modern hearing aids make use of devices for classification of hearing situations. The transmission parameters of the hearing aid are varied automatically depending on the hearing situation. In the process, the classification may influence, inter alia, the method of operation of the interference noise suppression algorithms, and the microphone system. First, as an example, a choice is made on the basis of the identified hearing situation (discretely switched or continuously superimposed) between an omnidirectional directional characteristic (zero-order directional characteristic) and considerable directionality of the microphone system (first order or higher order directional characteristic). The directional characteristic is produced by using gradient microphones or by electrically interconnecting two or more omnidirectional microphones. Microphone systems such as these have a frequency-dependent transmission response, which is characterized by a considerable drop at low frequencies. The noise response at the microphones is, on the other hand independent of frequency. To achieve a natural sound impression, the high-pass frequency response of the microphone system has to compensate for this by amplification of the low frequencies. The noise that is present in the low frequency range is likewise also amplified in the process and in some circumstances is clearly audible in a disturbing manner, while quieter sounds are concealed by the noise. Furthermore, in the case of a microphone system which is formed from two or more omnidirectional microphones, the microphone noise is higher than that with an individual omnidirectional microphone, with the microphone noise increasing with the number of omnidirectional microphones being used.
PCT Application WO 00/76268 discloses a hearing aid having a signal processing unit and at least two microphones, which can be interconnected in order to form different order directional microphone systems, in which case the directional microphone systems themselves can be interconnected with a weighting that is dependent on the frequency of the microphone signals emitted from the microphones. The cut-off frequency between adjacent frequency bands in which different weighting of the microphone signals occurs can be adjusted as a function of the result of signal analysis.
European Application 0 942 627 discloses a hearing aid having a directional microphone system with a signal processing device, an earpiece and two or more microphones, the output signals of which can be interconnected via delay devices and the signal processing device with different weightings in order to produce an individual directional microphone characteristic. The preferred reception direction (main direction) can be adjusted individually in the directional microphone system for matching to the existing hearing situation.
U.S. Pat. No. 5,524,056 discloses a hearing aid having an omnidirectional microphone and a first order or higher order directional microphone. The amplitude of the microphone signal from the directional microphone is amplified in the low signal frequency range, and is matched to the microphone signal from the omnidirectional microphone. Both the microphone signal from the omnidirectional microphone and the microphone signal from the directional microphone are supplied to a switching unit. The omnidirectional microphone is connected to a hearing aid amplifier when the switching unit is in a first switch position, and the directional microphone is connected to the hearing aid amplifier when the switching unit is in a second switch position. The switching unit can switch automatically as a function of the signal level of a microphone signal.
One disadvantage of the known hearing aids with a directional microphone system is that, in certain hearing situations, either the directionality of the microphone system is not optimally used or a high degree of directionality leads to a clearly audible deterioration in the sound quality.